A huge leak of confidential documents has revealed how the rich and powerful use tax havens to hide their wealth.

Eleven million documents were leaked from one of the world's most secretive companies, Panamanian law firm Mossack Fonseca.

They show how Mossack Fonseca has helped clients launder money, dodge sanctions and evade tax.

The company says it has operated beyond reproach for 40 years and has never been charged with criminal wrong-doing.

The documents show links to 72 current or former heads of state in the data, including the Icelandic Prime Minister, Sigmundur Gunnlaugson, who had an undeclared interest linked to his wife's wealth and is now facing calls for his resignation.

The files also reveal a suspected billion-dollar money laundering ring involving close associates of President Putin.

Gerard Ryle, director of the International Consortium of Investigative Journalists (ICIJ), said the documents covered the day-to-day business at Mossack Fonseca over the past 40 years.

"I think the leak will prove to be probably the biggest blow the offshore world has ever taken because of the extent of the documents," he said to foreign media.

The documents also shed light on how Mossack Fonseca offered financial services designed to help business clients hide their wealth, foreign media reports.